1. Field of the Invention
The present invention relates to an image forming method and an image forming apparatus capable of forming images on both sides of a sheet or recording medium.
2. Description of the Background Art
A copier, printer, facsimile apparatus or similar image forming apparatus of the type operable in a duplex print mode, i.e., capable of forming images on both sides of a sheet is conventional. It is a common practice with this type of apparatus to transfer a toner image from an image carrier to one side of a sheet, fix the toner image, reverse the sheet via a reverse path, and again feed the sheet for forming a toner image on the other side of the sheet. This kind of scheme, however, lacks reliability in sheet conveyance because a sheet is curled due to the switching of a path and the fixation of a toner image carried on one side of the sheet.
Japanese Patent Laid-Open Publication No. 1-209470, for example, discloses an image forming apparatus constructed to transfer toner images to both sides of a sheet by use of a first and a second image carrier and then fix the toner images at the same time. More specifically, first image transferring means transfers a first toner image from a photoconductive element to an image transfer belt and then transfers a second toner image from the photoconductive element to one side of a sheet. Subsequently, second image transferring means transfers the first toner image from the image transfer belt to the other side of the sheet. The sheet carrying the toner images on both sides thereof is conveyed to a fixing device.
However, the problem with the apparatus taught in the above document is that the image transfer belt must make two turns to print the toner images on both sides of the sheet. More specifically, the second toner image begins to be formed only after the image transfer belt has completed one turn, resulting in low productivity in the duplex print mode.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 6-27757 and 10-104963.
It is an object of the present invention to provide an image forming method and an image forming apparatus capable of executing the duplex print mode without lowering productivity.
In accordance with the present invention, an image forming apparatus is operable in a duplex print mode for printing images on both sides of a recording medium. A toner image is transferred from a first image carrier to a second image carrier and then transferred from the second image carrier to one side of the recording medium. Subsequently, a toner image is transferred from the first image carrier to the other side of the recording medium. After the toner image has been transferred from the first image carrier to the second image carrier, the second image carrier is moved in the reverse direction to a preselected position.
Also, in accordance with the present invention, an image forming method transfers, in a duplex print mode, a toner image from a first image carrier to a second image carrier and then transfers the toner image from the second image carrier to one side of a recording medium. The method then transfers a toner image from the first image carrier to the other side of the recording medium to thereby print images on both sides of the recording medium. After the toner image has been transferred from the first image carrier to the second image carrier, the second image carrier is moved in the reverse direction to a preselected position.